This invention relates generally to control valves, and more specifically, to a manually set control valve of the type used in a fluid control system such as a safety system for oil and gas wells.
The control valve of the invention is contemplated for use in safety systems which shut in well production lines or other flowlines in the event of unduly high or low pressure conditions in the main flowline. The general configuration of this type of safety system is generally shown in U.S. patent application Ser. No. 057,490 filed on July 13, 1979, now U.S. Pat. No. 4,256,146 by Peters. In the event of an abnormal pressure condition in the main flowline, the control valve moves from its unseated position to its seated position in which no fluid flows to the actuator. In response to the stoppage of fluid flow, the actuator closes the shut-off valve in the main flowline. A resumption of fluid flow to the actuator, which results in the opening of the shut-off valve, will occur upon the manual movement of the control valve to its unseated position.
For safety reasons, it is highly desirable that the control valve remains in the seated position until it is manually reset. A resumption of pilot pressure alone should not open the control valve.
Heretofore, arrangements used to achieve a so-called "lock out" of the control valve require an unduly complex valve structure, and rely on close tolerances and the integrity of O-ring seals to establish the necessary pressure conditions in the valve. These arrangements are exemplified by U.S. Pat. No. 4,145,025 issued to Bergeron on Mar. 20, 1979, U.S. Pat. No. 4,004,610 issued to Theriot on Jan. 25, 1977, U.S. Pat. No. 3,877,484 issued to Theriot et al on Apr. 15, 1975, and U.S. Pat. No. 4,094,340 issued to Bergeron on July 13, 1978. It is desirable that the control valve achieve a "lock out" when in the seated position without relying on close tolerances or the integrity of O-ring seals.